Stroboscope



Oct. 11, 1938. HAMACHER 2,133,138

STROBOSCOPE Filed May 4, 1936 Fig.2. 4

za 24 /6 l4 2/ l mg n II In 4mm lllllll VACUUM TUBE 1 4 OSCILLATOR Inventor Fritz I-Iam acher,

Patented Oct. 11, 1938 2,133,138

UNITED STATES PATENT OFFICE STBOBOSCOPE Fritz Hamacher, Spandau-Ruhleben, Germany,

assignor to General Electric Compa y, a corporation of New York Application May 4, 1936, Serial No. 77,880 In Germany May 24, 1935 13 Claims. (Cl. 88-14) My invention relates to stroboscopes and conarrangement between them and the relative voltcerns particularly such apparatus for viewing age applied is such as to diverge the cathode rays very rapidly moving objects. emanating from the cathode M.

It is an object of my invention to provide means The tube is energized by a source of current l8 for producing light flashes having a very high connected between the cathode l4 and the anode 5 order of frequency. It. Suitable means are provided for interrupt- Other and further objects and advantages will ing the cathode rays intermittently in order to become apparent as the description proceeds. cause intermittent energization of the fluorescent In accordance with my invention in itsprescreen i3, thereby producing light flashes for ferred form, I employ a cathode ray tube having stroboscopic purposes. If desired, the interrup- 10 a fluorescent screen and means for causing cathtion of the cathode rays may be produced by makode rays to impinge on the fluorescent screen ining the energizing current source la a source of termittently with a high frequency. The tube is alternating current. I so arranged that the fluorescent screen projects In the arrangement of Fig. 1, I provide a voltthe light upon the rapidly moving object to be age divider I9 connected between the terminals 15 Viewed provides a luminous background fo i of the current source l8 and connect the control houetting the moving object. electrode IT to an intermediate point on the volt- The invention Wi l be understood more rea y age divider I9. The relative voltages of the elecfrom the following detailed s pt W en oo trodes l6 and I! are such as to spread the cathode sidered in connection with the accompanying rays into a cone or a solid angle covering the 20 drawing and those features of the invention which screen l3. Inasmuch as the ratio of the instanare believed to be novel and patentable will be taneous voltages applied to the control electrode pointed out in h l m pp nd re In and the anode l6 determines the focusing or dethe drawin F 1 is a s hem t a m rep gree of divergence of the cathode rays, it will be senting one em d f my invention and apparent that the focusing of the rays and the 25 Fig. 2 is a schematic diagram representing a mOdilluminated area of the fluorescent screen I3 is ification of the apparatus of Fig. 1. Like referunchanged by the variations in instantaneous ence characters are utilized in the drawing to value of the voltage of the sourcei8. It will be designate ke parts throughout. understood that, when the instantaneous value In the arrangement of Fig. 1. an elec ronic tube of the voltage falls below zero, or, in fact, below 30 I is empl ye h vin a evacuated nv l pe l a given positive value, the emission of cathode containing a fluorescent screen 13 at one end and rays will be cut ofi and the screen l3 will become a cathod H at he other end producing radidark. The frequency of the light flashes produced an n r y. pr er cathode r or electrons by the fluorescent screen will, therefore, coincide impinging p the Screen T de M with the frequency of the alternating-current 35 is preferably of the incandescent type having a ur is, source of current l5 for heating t Cathode to The light produced by the fluorescent screen 13 incandescence. If an incandescent cathode is i u d to illuminate a, moving object which is empl y d h envelope y be evacuated t pto be observed. Such a moving object may, for

proximately 301 micron on the other hand example, be a rotating gear 20. If desired, the 40 with a cold cathod air pressures as high as 5 brilliancy of the fluorescent screen I 3 may be to 15 m crons ay be desirable- The tube ll y diminished by weakening the cathode rays and be similar to the known cathode ray tubes or to t rotating gear 20 may be observed by arrang- Braun tubes but preferably the cathode I4 is of ing the apparatus to bring the gear 20 between relatively increased size and the other electrodes th fluorescent screen l3 and the observers eye are suitably arr n to produce alight source f 2|, thus silhouetting the gear 20 against the flul'elat e y large area at the fluorescent Screen orescent screen 13. When used for silhouetting, by having t cathode rays emerge in a divergent the surface of the screen I3 is preferably of such fan or conep bundle Spread over substanarea as to subtend as great an optical angle as tially the entire surface of the screen l3. In addithe moving object to be observed, such as the gear tion to the cathode I4, an anode I6 is provided 20 or one of the teeth thereof.

and preferably also a control electrode II. In It will be understood that, in viewing moving the arrangement of Fig. 1, the anode l6 and the objects stroboscopically, the object may be made control electrode I! are in the form of perforated to appear to stand still or to move very slowly by 5 disks, diaphragms or cylinders and the spacial illuminating it with light flashes having the same of the speed of revolution, speed of vibration, or in the case of gears and similar objects with repeated similar parts such as spokes or teeth the angular speed divided by the number of spokes, teeth, or other repeated parts. In order to adapt the apparatus for observation of parts moving at different speeds, it is desirable to employ means for varying the frequency of the light flashes. For this purpose a suitable variable frequency alternating current source may be employed at I 8, e. g. a variable frequency vacuum tube oscillator such as illustrated in Fig. 2.

Although I have found that satisfactory results may be obtained by utilizing an alternating current energizing source to produce the interruptions in the illumination of the fluorescent screen, it will be understood that my invention is not limited to this precise arrangement. My invention obviously includes other means for interrupting the energization of the fluorescent screen, such as means for causing cathode rays to sweep across the fluorescent screen or around a target protecting the screen, or means for interrupting the voltage applied to a control electrode.

For example, in the arrangement of Fig. 2, I have shown a cathode ray tube ll having a cathode I4 and an anode 3 corresponding to the cathode and anode of the apparatus of Fig. 1 but energized by a direct-current source 22. The tube of Fig. 2 has two auxiliary electrodes which might be termed control electrodes", one of which, the electrode 23, serves as a focusing electrode for controlling the focusing of the cathode rays and is connected to an intermediate tap of the direct-current source 22, and the other of which, in the form of a grid 24, is arranged to cut off the cathode rays in the usual manner by interposing a negative electrostatic field. The control electrode 24 may be utilized to produce intermittent illumination of the fluorescent screen [3 by connecting a variable frequency alternating-current source 25 between the cathode l4 and the control electrode 24. Cathode rays will be caused to impinge upon the fluorescent screen l3 with a frequency corresponding to the frequency of the variable frequency source 25 since, whenever the voltage of this source becomes negative, the cathode rays will be cut oil. Inasmuch as stroboscopes employing cathode ray energized fluorescent screens are of particular value for observing extremely high frequency phenomena for the reason that cathode rays lend themselves to control at considerably higher frequencies than the frequencies of light flashes which have hitherto been available in stroboscopic apparatus, I prefer to provide a source of high frequency, such as a vacuum tube oscillator, for energizing the control electrode 24. Some portion of the vacuum tube oscillator circuits, such as an inductance or a condenser 26 may be made variable, and may be provided with a control handle extending from the casing of the oscillator 25 or with other suitable means to permit varying the frequency of the light flashes illuminating the moving object 20.

If desired, instead of actually interrupting cathode rays for the purpose of producing light flashes from the fluorescent screen I3, I may cause the cathode rays to sweep across the fluorescent screen I3. For example, by adding electromagnetic beam control means, such as a coil, or electrostatic beam control means, such as a pair of deflecting plates 21, energized by a suitable source of alternating current 28, I may cause the beam 2,138,138 frequency or a frequency nearly the same as that to sweep back and forth across the fluorescent screen l3. Preferably, in this form, of the invention, the cathode l4 and the electrodes 23 and 24 are so shaped as to produce a flat beam in the form of a sheet of cathode rays in a plane perpendicular to the plane of the paper as seen in Fig. 2. The beam is thus fan shaped with the cathode rays spread across the solid angle which is subtended by the screen 13. By employing a fast fluorescent screen, such as one comprising calcium tungstate, the illumination of the screen will persist for a very short period of time after the cathode ray beam has passed across the screen and will be darkened in the interval between successive sweeps of the beam across the fluorescent screen l3.

If desired the sweep plates 2'! may be so arranged in relation to the other electrodes that the cathode rays are swept beyond the fluorescent screen to insure intermittent cessation of illumination, or one or more targets 29 may be provided in one or more portions of the tube to intercept the cathode rays during a portion of each successive sweep.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its principle and showing its application but it will be obvious to those skilled in the art that many modifications and variations are possible and I aim, therefore, to cover all such modifications and variations as fall within the scope of my invention which is defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United Statesis:

1. In a silhouetting stroboscope, the combination of a cathode ray tube having a fluorescent screen, and means within the tube for producing cathode rays, spreading them across a solid angle covering the screen and producing impingement of said rays upon said screen intermittently at high frequency to form high frequency light flashes each extending over the area of said screen.

2. In a stroboscope for viewing rapidly moving objects, the combination of a cathode ray tube with a fluorescent screen for providing light, means for generating a divergent cone of cathode rays impinging on said screen and substantially covering it to cause it to produce light, and means for interrupting at a high frequency the impingement of cathode rays on said screen to cause the light thereof to occur in high-frequency flashes.

3. In a stroboscope for viewing rapidly moving objects, the combination of an electronic tube with a fluorescent screen for providing light, means within the tube for directing radiant energy against said fluorescent screen and spreading said radiant energy across substantially the entire surface of the screen to cause it to produce light over its area, and means for interrupting at a high frequency the impingement of radiant energy on said screen to cause the light thereof to occur in high-frequency flashes.

4. In a stroboscope for viewing rapidly moving objects, the combination of an electronic tube with a device for converting radiant energy into light, means Within the tube for directing a divergent cone of radiant energy against said device with the base of said cone substantially covering said device to cause it to produce light, and means for interrupting at a high frequency the impingement of radiant energy on said device to cause the light thereof to occur in high-frequency flashes.

5. In a stroboscope for viewing rapidly moving objects, the combination of an evacuated discharge tube containing a light-generating surface, and means also contained within the tube for simultaneously energizing substantially the entire area of said light generator with interruptions at high frequency.

6. In a stroboscope for viewing rapidly moving objects, the combination of a cathode ray tube with a fluorescent screen for producing light, means for generating a fan-shaped bundle of cathode rays impinging on said screen and extending across its width to cause it to produce a line of light, and means for sweeping said cathode ray bundle transversely to itself across said screen beyond an edge thereof at high frequency to illuminate the entire screen and leave it dark alternately thus causing the. light thereof to occur in high-frequency flashes.

7. In a stroboscope for viewing rapidly moving objects, the combination of a cathode ray tube with a fluorescent screen for providing light, means for generating a divergent cone of cathode rays impinging on said screen and substantially covering it to cause it toproduce light. and means for interrupting said cathode rays at a high frequency.

8. Ina stroboscope for viewing rapidly moving objects, the combination of a cathode ray tube with a fluorescent screen for providing light, an anode and a cathode, and a source of highfrequency alternating current directly connected between said electrodes.

9. In a stroboscope for viewing rapidly moving objects, the combination of a cathode ray tube with a fluorescent screen for providing light, an

anode. a cathode and a beam cut-off control elec-' trode, a source of high-tension current connected between said anode and cathode, and a source of high-frequency alternating current connected between said cathode and control electrode.

10. In a stroboscope for viewing rapidly moving objects, the combination of a cathode ray tube with a fluorescent screen for providing light, an anode, a cathode and a control electrode, a voltage divider, and a source of alternating current of high frequency connected to said anode and cathode and to said voltage divider, said control electrode being connected to an intermediate part of said voltage divider.

11. In a stroboscope for viewing rapidly moving objects, the combination of a cathode ray tube with a fluorescent screen for providing light, an anode and a cathode, a source of variable frequency alternating current directly connected between said electrodes, and means for varying the frequencythereof.

12. In a stroboscope for viewing rapidly moving objects, the combination of a cathode ray tube having a fluorescent screen, means within the tube for producing'a cathode ray beam extending across said screen and means for interrupting at high frequency impingement of said beam on said screen.

13. In a stroboscope arrangement for viewing rapidly moving objects, an evacuated discharge tube having a light generating surface, means contained within the tube for energizing intermittently at high frequency substantially the entire surface of said light generator simultane-' ously.

mrrz HAMACHER. 

